[glib] docs: Add G_ENABLE_DIAGNOSTIC

[Emmanuele Bassi <ebassi src gnome org>]

commit 9453b97e098024a6138623acbb750f5d068ed54d
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Fri Feb 9 19:34:40 2018 +0000

    docs: Add G_ENABLE_DIAGNOSTIC
    
    We need to mention this environment variable, so that developers have a
    fighting chance of actually using it.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=732184

 docs/reference/glib/running.xml | 10 ++++++++++
 1 file changed, 10 insertions(+)
---
diff --git a/docs/reference/glib/running.xml b/docs/reference/glib/running.xml
index a02ffa404..ef536f440 100644
--- a/docs/reference/glib/running.xml
+++ b/docs/reference/glib/running.xml
@@ -244,6 +244,16 @@ How to run and debug your GLib application
   </para>
 </formalpara>
 
+<formalpara id="G_ENABLE_DIAGNOSTIC">
+  <title><envar>G_ENABLE_DIAGNOSTIC</envar></title>
+
+  <para>
+    If set to a non-zero value, this environment variable enables
+    diagnostic messages, like deprecation messages for GObject properties
+    and signals.
+  </para>
+</formalpara>
+
 </refsect2>
 
 <refsect2 id="setlocale">